Fastener driving tool

ABSTRACT

There is provided a fastener driving tool having a control valve actuated only by the combined operation of a trigger device and a safety device. The control valve is used to open and close a known type of cylinder valve. A cycling valve is incorporated into the control valve so that the tool will operate through both a drive and return stroke automatically regardless of whether the trigger device and safety device have been released.

United States Patent [1 1 3,685,396 Obergfell [451 Aug. 22, 1972 [54] FASTENER DRIVING TOOL 3,278,104 10/ 1966 Becht et a1 ..9l/220 72 Inventor: Allen R obergfeu, p Ridge [IL 3,375,758 4/1968 Novak et a1. ..91/356 3,427,928 2/1969 Bade ..9 U356 [73] Asslgnee: Fastener Corporation, Franklin Park, 111.

[22] Filed: June 1970 Primary Examiner-Paul E. Maslousky [21] Appl. No.: 48,867 Attorney-Mason, Kolehmainen, Rathburn & Wyss Related US. Application Data [63] Continuation of Ser. No. 767,020, Aug. 26,

1968, abandoned, which is a continuation-in- ABSTRACT part of 1966 aban' There is provided a fastener driving tool having a condoned trol valve actuated only by the combined operation of a trigger device and a safety device. The control valve [52] US. Cl ..91/356, 91/399, 91/gl1/716Al, is used to Open and close a known typa of cylinder valve. A cycling valve is incorporated into the control [51] Int. Cl. ..Fl5b 114/15, Fl5b91i/617 valve so that the tool will Operate through both a drive [58] Fleld of Search""9l/220 17 3 2 6 and return stroke automatically regardless of whether I the trigger device and safety device have been [56] References Cited released UNITED STATES PATENTS 3,278,103 10/1966 .luilfs (it al ..91/220 31 Claims, 12 Drawing Figures i 46 64 46 2 65 I i 1 6} 0 1 i ms 66 1 1 2 26 a ,4; 4 l K t 777 Q; y 84 I 6 ,7 31%,; 10% ,1;

l i ms 9 l 66 1 i 1 ii k T 1 m" I I l I H PATENTED M1822 I972 sum 1 0r 5 L m W M 2 Aw Wa on,

PATENTEDAUG22 I972 SHEET 2 0F 6 Arrow/5Y5.

FASTENER DRIVING TOOL This invention relates to a fastener driving tool and, more particularly, to a fastener driving tool including new and improved control means and control means for a fastener driving tool. The present application is a continuation of an application Ser. No. 767,020, filed Aug. 26, 1968, now abandoned, which application is a continuationin-part of copending application Ser. No. 602,991 filed Dec. 19, 1966, now abandoned.

Commercial pneumatic fastener driving tools on the market today are generally of the type operated by a trigger actuated pilot valve that function, when the trigger is depressed, to move the drive piston and connected fastener driving blade through a power or drive stroke of a fastener driving operation by admission of pressurized fluid into the cylinder of the tool. The drive piston will generally remain at the end of its power stroke until the fluid pressure in the cylinder is released, as by exhausting the cylinder to the atmosphere, at which time piston return means becomes effective to return the piston to its normal or static position. Moreover pneumatic fastener driving tools are known wherein the drive piston and driving blade move both up and down automatically upon depression of the trigger, before the trigger is released; for example, one such tool is described and claimed in Letters Patent of The United States No. 3,353,453 that issued Nov. 21, 1967 and is assigned to the assignee of the present invention. This snap-action or automatic single-cycle piston and driving blade operation is desirable in many applications such as upholstery stapling to prevent fraying of the material by the working blade while the tool is moved along the workpiece.

Fastener driving tools also are known which are provided with a safety valve arrangement wherein the tool cannot be made to fire or operate through a driving stroke unless the nosepiece of the tool is held against the workpiece. Heretofore separate control valves have generally been incorporated into commercial fastener driving tools to perform the pilot valve function, the safety valve function, and the single-cycle valve function. Such incorporation of separate valves, while performing satisfactorily, requires space and adds weight, in addition to increasing the cost of a fastener driving tool.

Fastener driving tools, and particularly the snap-acting or automatic single-cycling tools, may be susceptible to sporadic multiple firing during recoil of the tool. The tendency toward such sporadic multiple firings may be more pronounced where the tool includes an actuating lever or safety lever in engagement with the workpiece for controlling the firing of the tool.

Accordingly one object of the present invention is to provide a new and improved pneumatically actuated fastener driving tool.

Another object of the present invention is to provide a fastener driving apparatus including a new and improved control means which incorporates the pilot valve, the safety valve, and the single-cycle valve into a single valve assembly.

Yet a further object of the present invention is the provision of a new and improved control valve for a fastener driving tool which incorporates the pilot valve and the safety valve into a single control valve assembly.

Yet a further object of the present invention is the provision of a fastener driving tool having a new and improved control valve which is small in size, light in weight, and economical to manufacture.

Yet another object of the present invention is the provision of a fastener driving tool wherein the tendency toward sporadic multiple firing of the tool is minimized.

In accordance with these and many other objects, there is provided a new and improved single-cycle control valve for a pneumatically operated fastener driving tool. The control valve is particularly adapted for use in a pneumatically actuated fastener driving tool of the type including a housing having a cavity defining a fluid reservoir and having a piston slideably mounted within a cylinder in the housing to provide for the driving force of the fastener driving too]. Cylinder valve means control the admission of fluid to and the exhaustion of fluid from one end of the cylinder. In accordance with the present invention there is provided an improved control valve assembly including a trigger control means and a safety control means and responsive to joint actuation of both trigger control and the safety control. Additionally, in a preferred embodiment, the control means has incorporated a single-cycle valve to provide for snap'action firing of the tool.

In an illustrated embodiment of the invention, the control valve includes a valve cylinder defined in the tool housing with a valve piston slideably received in the valve cylinder. The valve piston is closed at one end to define a valve chamber and is provided with an exhaust opening at the other end defining a valve seat. A pilot valve element is provided in the chamber. Both the valve piston and the pilot valve element are each provided with respective valve stems extending out of opposite ends of the valve cylinder. One of the stems is engageable by depression of the trigger of the fastener driving tool, while the other valve stem is engageable by the safety valve control of the tool. The valve piston and pilot valve element are positioned to be actuated relative to each other only upon the joint actuation of both the trigger and the safety control.

Further in accordance with a preferred embodiment of the invention, the improved control valve includes a single-cycle valve stem member within the chamber defined within the valve piston to provide for snap-acting operation of the fastener driving tool.

In accordance with another feature of the present invention, there is provided a lost motion connection between the safety trigger or lever which is normally in engagement with the workpiece and the valve controlled thereby so that any tendency towards sporadic multiple firing of the tool due to recoil is Many other objects and advantages of the present in vention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. I is a fragmentary cross sectional view of a fastener driving tool incorporating the improved singlecycle control valve according to the present invention and illustrated with the drive piston and driver blade in its static or at rest position;

FIG. 2 is a fragmentary cross sectional view of the fastener driving tool of FIG. 1, taken through the control valve along line 2--2 of FIG. 1;

FIG. 3 is a fragmentary cross sectional view of the fastener driving tool of FIG. 1, illustrating the control valve thereof in cross section, and drawn to a larger scale than FIG. 1;

FIG. 4 is a fragmentary cross sectional view of the fastener driving tool of FIG. 1, illustrating a cross sectional view of the control valve assembly, and illustrated with the control valve assembly in the firing position;

FIG. 5 is a fragmentary cross sectional view of the fastener driving tool of FIG. 1, illustrating the control valve assembly in cross section, and shown after the completion of the cycling of the drive piston, but before release of the trigger and safety controls;

FIG. 6 is a fragmentary cross sectional view of a fastener driving tool incorporating a modified form of control valve according to the present invention and illustrating the control valve when the drive piston and driver blade are in their static or at rest positions;

FIG. 7 is a fragmentary cross sectional view of the fastener driving tool of FIG. 6 illustrating the control valve when the drive piston and driver blade are in their firing positions;

FIG. 8 is a fragmentary cross sectional view of a fastener driving tool incorporating a modified singlecycle control valve according to the present invention illustrated with the drive piston and driver blade in their static or at rest position;

FIG. 9 is a fragmentary cross sectional view of the fastener driving tool of FIG. 8 illustrating the control valve drawn to a larger scale;

FIG. 10 is a fragmentary view of the control valve and valve housing of the tool of FIG. 8;

FIG. 11 is a fragmentary bottom view of the control valve illustrated in FIG. 8; and

FIG. 12 is a fragmentary cross sectional view of the control valve of FIG. 8, drawn to a larger scale.

Referring now to the drawings, and particularly to the embodiment of FIGS. 1 through 5, there is fragmentarily illustrated ,a fastener driving tool, generally illustrated as 10, which embodies a control valve assembly. according to the present invention. The tool 10 may be of known construction, and, as illustrated, comprises a housing 12 including a generally vertically extending head or forward portion 12a, FIG. 1, and a rearwardly extending hollow handle portion 12b defining a fluid reservoir 16. Pressurized fluid, such as compressed air, is supplied to the fluid reservoir of the tool by a suitable flexible line. The drive system for the tool 10 includes a main or power cylinder 18 mounted within the head portion 12a and having an open upper end 18a that is adapted to be selectively connected to the reservoir 16. The open upper end of the cylinder 18 is in engagement with a diaphragm-type main or cylinder valve assembly 20, here shown of the poppet type, under the control of a control valve assembly 22 according to the present invention. A fastener driving assembly 24 slideably mounted within the cylinder 18 includes a work or drive piston 26 and has connected thereto a depending driver blade member 28. The fastener driving assembly 24 is normally biased to a position with the piston 26 adjacent the cylinder valve assembly 20. An exhaust valve assembly indicated generally as 32 is provided for controlling the selective connection of the upper end of the cylinder 18 to the atmosphere.

When the tool 10 is to be operated, compressed fluid from the reservoir 16 enters the upper open end 18a of the cylinder 18 and drives the fastener driving assembly 24 downwardly to engage and set a fastener or nail supplied to a drive track 36 in anosepiece or nosepiece structure 38. The flow of compressed fluid into the upper end of the cylinder 18 is controlled by the main valve assembly 20, which includes a diaphragm 40, the periphery of which is clamped between a cap 42 and the head portion of the housing 12 and which seats against the upper edge 18a of the cylinder 18. The diaphragm 40 is resiliently biased against the upper edge surface 18a by a spring 44 located between the cap 42 and the diaphragm 40. The cylinder side of the diaphragm 40 is continuously in communication with the fluid reservoir 16 through a suitable passageway 46 so that pressurized fluid continuously acts against the cylinder side of the diaphragm 40 tending to displace the diaphragm 40 from the edge 18a of the cylinder 18. However pressurized fluid is also introduced to the opposite side of the diaphragm 40 through a passageway 48 while the fastener driving tool 10 is in a static or at rest position. The pressure acting on the diaphragm 40 is effective to maintain the diaphragm 40 in a closed position, as illustrated in FIG. 1. However if the pressurized fluid above the diaphragm 40 is discharged, the pressurized fluid acting through passageway 46 is effective to unseat the diaphragm 40 from the edge 18a of the cylinder 18 to dump pressurized fluid into the top of the main cylinder 18 and to drive the drive piston 26 through a drive stroke.

When the fastener driving tool is at rest, or during the return stroke of the drive piston, the upper open end of the cylinder 18 is exhausted to the atmosphere through the exhaust valve assembly 32. In the illustrated embodiment the exhaust valve assembly comprises a hollow valve stem 50 secured to the diaphragm and connecting the upper end of the cylinder 18 to atmosphere through a suitable exhaust passageway 52. However when the drive piston is operated through a fired or drive stroke, it is necessary for the upper end of the cylinder 18 to be closed, and to this end there is provided a valve seat 54 disposed adjacent the end of the valve stem 50 remote from the cylinder 18 and adapted-to be engaged by the valve stem 50 when the diaphragm 40 is raised at the initiation of a drive stroke, thereby closing off the upper end of the cylinder 18 to the atmosphere.

To provide for the return drive of the fastener driving assembly 27, there is provided an air return chamber 60 communicating with the lower end of the cylinder 18 through a plurality of ports 62. Moreover the drive piston 26 is provided with suitable one way valve means 63, which may be of the type more fully described in an application for Letters Patent of The United States Ser. No. 602,728 filed Dec. 19, 1966 and assigned to the assignee of the present invention. However, briefly, to this end the piston 26 is provided with spaced peripheral grooves 64 and 66, the upper one 64 of which serves as a sealing groove while the lower one 66 functions as the one way valve means 63 to provide for the bypass of pressurized fluid to the air return chamber 60. An O-ring 68 provided in the upper one of the grooves 64 functions as a sealing member effecting a pneumatic seal between the piston 26 and the inner wall of the cylinder 18. To bypass around the groove 64 and O-ring 68, there is provided a plurality of air passageways 71) extending from the lower one of the grooves 66 and communicating with a central cavity 26a in the piston 26. An O-ring 72 defining a valve element is positioned within the lower one of the grooves 66. The O-ring 72 is of resilient construction and is normally seated against the ports defined by the air passageways 70. The O-ring 72 is expandable upon a selected pressure differential between the upper and lower ends of the cylinder through the piston 26 so as to unseat from the ports of the air passageways 70 to provide for fluid to bypass through the piston 26 around the O-ring 72 and to supply air to the air return chamber 60.

It will be understood that in the operation of the basic tool, the piston 26 and associated driver blade member 28 is driven downwardly through a drive stroke by connection of the open upper end 18a of the cylinder 18 with the reservoir 16. Since there is no significant restraint to the piston 26 during its downward movement, the pressure above the piston 26 will not build up sufficiently to unseat the O-ring 72 until the piston 26 approaches the bottom of its drive stroke. At this point the pressure above the piston 26 will continue to build up until it approaches the pressure in the reservoir 16 and the O-ring 72, functioning as a valve element, will be unseated from the ports of the air passageways 70, thereby providing a source of pressurized fluid to the air return chamber 60 through the air passageway openings 62. Upon exhaustion of the open upper end 18a of the cylinder 18 to the atmosphere, the pressurized fluid in the air return chamber 68 will reenter the lower end of the cylinder 18 through the ports 62 and will drive the piston 26 back to its normal or at rest position.

To cushion the drive stroke of the piston 26, there is provided a resilient annual bumper 74 at the lower end of the cylinder 18 which is engageable by the piston 26 as it reaches the end of its drive stroke.

Referring now to the control valve assembly 22, in accordance with the present invention, the control valve assembly requires the cooperation of both a trigger 78 and a safety lever 80 to operate. Once either the trigger 78 or the safety lever 80 is positioned, the other can manipulate the cycle valve to fire the tool. Moreover, in accordance with the embodiment of FIGS. 1 through 5, the control valve assembly 22 includes a single-cycle mechanism which is efi'ective when the work piston has reached a predetermined position to return the work piston 26 to its normal or at rest position to condition the tool for a subsequent operation. Referring now specifically to the control valve assembly 22, the control valve assembly includes a valve cylinder 82 defined in the housing 12. A valve body 84 is slideably received within the valve cylinder 82 and includes a valve body stem or operator 86 extending out of the valve cylinder 82 and engageable by one of the control means, here shown as the safety lever 80, to shift the valve piston 84 within the valve cylinder 82. In the illustrated embodiment, the safety lever 80 is provided with a bifurcated end 800 receiving the stem 86 to provide a lost motion connection between the safety lever 80 and the valve body 84. The valve body 84 is closed at its lower end, as illustrated at 840, FIGS. 3, 4 and 5, to define a valve chamber 88.

The other end of the valve body 84 is provided with an exhaust opening 84b opening to the atmosphere through the valve cylinder 82 and an exhaust port 90, FIG. 2. The exhaust opening 84b is formed in part by an O-ring 92 defining a valve seat.

A control or trigger valve element 94 contains a valve head 94a normally seated on the valve seat 92 and separable therefrom upon actuation of both the control means, the trigger 78, and the safety lever 80. To this end the trigger valve 94 includes a valve stem or operator 96 extending through the open end of the valve body 84. A compression spring 97 biases the head 94a of the trigger valve 94 closed against the valve seat 92. The valve stem 96 may be actuated by the trigger 78 through a trigger rod 98 and a trigger lever 100. A spring 102 positioned between the housing 12 and trigger 78 is effective to bias the trigger 78 into its released position.

To provide for a plurality of passageway chambers between the valve body 84 and the valve cylinder 82, the valve body 84 is provided with a plurality of sealing rings 104, 106, 108 and 110 defining first, second, and third passageway chambers 112, 114, and 116. The first passageway chamber 112 is always in communication with the cylinder valve assembly 20 through the passageway 48. The second passageway chamber 114 is always in communication with the fluid reservoir 16 through a passageway 118. The third passageway chamber 116 is connected to receive a signal as to the position of the piston 26 and, in the illustrated embodiment, is in communication with the air return chamber 60 through a passageway 120.

To provide for the snap acting of the piston 26, there is provided a single-cycle valve member 122, FIGS. 3, 4, and 5, positioned within the valve chamber 88. The valve member 122 includes a valve stem 124 containing a pair of spaced heads 126 and 128 each defining piston means. The lower one of the valve heads 128 contains a sealing ring 130 to form a pneumatic seal between the valve member 122 and the inner wall of the valve chamber 88 while the upper one 126 of the valve heads is a comparatively loose fit within the valve chamber 88 to provide for a small seepage of fluid around the head. Moreover the valve piston 84 contains a first opening or port 132 communicating between the valve chamber 88 and the first passageway chamber 112 and therefore always in communication with the cylinder valve assembly 20 through the passageway 48. The valve body 84 is also provided with a second opening 134 communicating between the valve chamber 88 and the second passageway chamber 114 and therefore always in communication with the air reservoir 16 through the passageway 118. In addition the valve piston body 84 contains a third opening 136 communicating between the valve chamber 88 and a third passageway chamber 1 16 and always in communication with the air return chamber 60 through the passageway 120. The upper one of the valve heads 126 is positioned to cross over the first opening 132 in the valve body 84 during the stroke of the valve member 122, while the lower one of the valve heads 128 is positioned intermediate the second and third openings 134 and 136 in the valve body 84 during the stroke of the valve member 122.

From the above detailed description, the operation of the improved control valve assembly is believed clear. However, briefly, when the fastener driving tool 10 is at rest as indicated in FIGS. 1 and 3, fluid from the reservoir 16 entering through the opening 134 enters the valve chamber 88 and seeps around the valve head 126 and the valve piston 84, passing through the opening 132 into the first passageway chamber 112 and through the passageway 48 to provide pressurized fluid to the cylinder valve assembly 20 to maintain the valve closed.

When it is desired to fire the tool 10 through a work cycle, it is necessary to depress both the safety lever 80 and the trigger 78 in order to unseat the head 94a of the trigger valve 94 from the valve seat 92. At this time the pressurized fluid from the cylinder valve assembly 20 is bled through the passageway 48, passageway chamber 112, opening 132, around the trigger valve 94 and exhausted through the exhaust port 90. The seepage of pressurized fluid between the valve head 126 and the valve body 84 is insufficient to appreciably afi'ect the exhaust of fluid from the cylinder valve assembly 20. The position of the control valve assembly components 22 during this firing stroke are illustrated in FIG. 4. It will be understood that as the work piston 26 is driven downwardly, pressurized fluid will begin to accumulate in the air return chamber 60. The pressure in the air return chamber 60 is transmitted to the control valve assembly 22 through the passageway 120.

To provide for the snap-acting return of the work piston 26, as soon as a sufficient signal is received from the air return chamber 60 through the passageway 120, the pressure is transmitted into the chamber 88 below the single-cycle valve member 122 through the third passageway chamber 116 and the third opening 136. This pressure is effective to overcome the downward bias of pressure from the reservoir 16 acting on the sealing ring 130 and the single-cycle valve member 122 will be driven upwardly to the position illustrated in FIG. 5. At this time pressurized fluid entering through the passageway 118 and second passageway chamber 114 will enter into the valve body 84 through the second opening 134. The force of this pressure will be transmitted substantially unrestricted to the first opening 132 into the first passageway chamber 112 and through the passageway 48 to the cylinder valve assembly 20 to close the cylinder valve assembly 20 and permit return of the work piston 26 by the fluid in the air return chamber 60.

Since the air above the single-cycle valve element 122 will dump to the atmosphere through the exhaust port 90, there will not be sufficient downward bias on this valve element to return it to its normal position, and the single-cycle valve element 122 will remain in the return position illustrated in FIG. until such time as either the trigger 78 or safety lever 80 is released. At that time the components of the control valve assembly 22 will return to the normal or at rest position. 7

The tool may be actuated only by operation of bath the trigger 78 and the safety lever 80. Moreover in a particular embodiment of the invention it was found that the valve element 96 had to be depressed only 0.010 inch or 0.015 inch to fire the tool. Therefore the lost motion connection between the valve body 84 and the safety lever 80 has been provided. The lost motion 8 connection is dependent upon the length of the piston stem 86, and permits recoil of the tool without firing through the safety lever thus resulting in a tool which is less susceptible to sporadic multiple firing.

If desired a combination safety and trigger control valve assembly may be provided without the singlecycle arrangement heretofore described. Such a dual purpose control valve assembly is illustrated in FIG. 6 in its normal or at rest position and in FIG. 7 in its fired position. As therein illustrated, a control'valve assembly 140 is adapted to be installed in a housing 141 of a tool, not fully shown but which may be otherwise similar to tool 10 illustrated in the embodiment of FIGS. 1 through 5. The control valve assembly 140 is adapted to be operated by the cooperative movement of a trigger 142 and a safety lever 143. More specifically the control valve assembly includes a valve cylinder 146 containing a valve body 148 received therein and having a valve stem or operator 150 extending therefrom. The valve body 148 is closed at its stem end to define a valve chamber 152 and is provided with an exhaust opening or port 154 atits opposite end. An O-ring 156 around the exhaust opening 154 defines a valve seat. A trigger valve 158 is contained within the chamber 152, and is provided with a head 160 adapted to seat against the valve seat 156. The other end of the valve member 158 also defines a valve element 162 adapted to seat against a valve seat 164 intermediate the length of the valve chamber 152. The trigger valve 158 additionally includes a stem or operator 166 extending out of the valve body 148 through the exhaust port 154.

It is understood that the control valve assembly 22 may be connected so that the safety lever 143 actuates the trigger valve 158 .while the trigger 142 controls the displacement of the valve body 148, as illustrated in FIGS. 6 and 7, through a trigger rod 168 and a trigger lever 170. If desired, however, the position of the control valve assembly 140 may be reversed relative to the trigger 142 and safety lever 143, as more fully described in the embodiment of FIGS. 1 through 5. A compression spring 172 interposed between the lever and the cylinder 146 biases the trigger 142 to its released position.

Referring now to the valve body 148, the valve piston 148 is provided with a plurality of sealing rings 174, 176, and 178 to define first and second passageway chambers 180 and 182 therebetween. The first passageway chamber 180 is in communication with the end portion of the valve chamber 152 remote from the valve seat 164 through a piston passageway 184, and further communicated with a fluid reservoir 16 through a suitable fluid passageway 186 defined in the valve cylinder 146. The second passageway chamber 182 is in communication with the valve chamber 152 intermediate the valve seats 156 and 164 through a piston passageway 188, and is further in communication with the cylinder valve assembly (not shown) through a suitable fluid passageway 190.

From the above detailed description, the operation of the control valve assembly 140 according to the present invention is believed clear. However, briefly, with the fastener driving tool at rest, the parts of the control valve assembly 140 are in the position illustrated in FIG. 6. At this point the head 160 of the trigger valve 158 is closed against the valve seat 156 while the valve element 162 is unseated from the valve seat 164. Pressurized fluid from the reservoir may now enter through the passageway 186, the passageway chamber 180, and the passageway 184 into the valve chamber 152, around the valve seat 164 and be directed to the cylinder valve assembly through the passageway 188, the passageway chamber 182, and the fluid passageway 190. Depression of only one of the control members, that is, either the trigger 142 or the safety lever 143, will be ineffective to unseat the valve head 160 from the valve seat 156. However upon depression of both the control elements, the trigger valve 158 will be displaced relative to the valve piston 148 so that the head 160 of the trigger valve 158 is displaced from the valve seat 156 and at the same time the valve element 162 seats upon the valve seat 164 to separate the upper and lower portions of the valve chamber 152. In this position, fluid from the cylinder valve assembly is exhausted to the atmosphere through the passageway 190, the passageway 188, and around the valve seat 156 through the exhaust port 154.

Upon release of either the trigger 142 or the safety lever 143, the trigger valve 158 will return to the position illustrated in FIG. 6 with the valve head 160 seated against the valve seat 156. The valve element 162 will unseat from the valve seat 164. Pressurized fluid from the reservoir 16 will now enter through the passageway 186, passageway chamber 180, passageway 184, into the valve chamber 142, and through the passageway 188, passageway chamber 182, and passageway 190 to act upon and close the cylinder valve assembly, permitting the work piston 26 to return to its normal or at rest position.

FIGS. 8 through 12 illustrate another embodiment of the control valve applied to a modified form of fastener driving tool wherein the piston return chamber of the tool is defined by a differential piston operating in a differential diameter cylinder. Referring now to the embodiment of FIGS. 8 through 12, there is fragmentarily illustrated a modified fastener driving tool, generally illustrated as 210, which embodies a control valve assembly according to another embodiment of the present invention. The tool 210 may be of known construction, and, as illustrated, is similar to that illustrated and described in Wandel US. Pat. No. 3,208,353 granted Sept. 28, 1965. However, briefly, the tool 210 includes a housing 212 having a generally vertically extending head or forward portion 212a, FIG. 8, and a rearwardly extending hollow handled portion 2l2b defining a fluid reservoir 216. The drive system for the tool 210 includes a main or power differential type cylinder 218 mounted within the head portion 212a of the cylinder having an open upper end 218a that is adapted to be selectively connected to the reservoir 216. The open upper end of the cylinder 218 is in engagement with a diaphragm-type main or cylinder valve assembly 220, which may be identical with the cylinder valve assembly heretofore described, under the control of a control valve assembly 222 according to the present invention. A fastener driving assembly 224 slideably mounted within the cylinder 18 includes a differential type work or drive piston 226 and has connected thereto a depending driver blade member 228. The fastener driving assembly 224 is normally biased to a position with the piston 226' adjacent the cylinder valve assembly 220. An exhaust valve assembly generally indicated as 232 is provided for controlling the selective connection of the upper end of the cylinder 218 to the atmosphere. The exhaust valve assembly 232 may be identical with the exhaust valve as sembly 32 heretofore described.

When the tool 210 is to be operated, compressed fluid from the reservoir 216 enters the upper end 218a of the cylinder 18 and drives the fastener driving assembly 224 downwardly to engage and set a fastener or nail supplied to a drive track 236 in a nosepiece or nosepiece structure 238. The flow of compressed fluid into the upper end of the cylinder 218 is controlled by the main valve assembly 220, which includes a diaphragm 240 seatable against the upper edge 218a of the cylinder 218. The diaphragm 240 is resiliently biased against the upper edge surface 2180 by a spring 244 located between a cap 242 and the diaphragm 240. The cylinder side of the diaphragm 240 is continuously in communication with the fluid reservoir 216 through a suitable passageway 246 so that pressurized fluid continuously acts against the cylinder side of the diaphragm 240 tending to displace the diaphragm 240 from the edge 218a of the cylinder 218. However pressurized fluid is also introduced to the opposite side of the diaphragm 240 through a passageway 248 while the fastener driving tool 210 is in a static or at rest position. The pressure acting on the diaphragm 240 is effective to maintain the diaphragm 240 in a closed position, as illustrated in FIG. 8. However if the pressurized fluid above the diaphragm 240 is discharged, the pressurized fluid acting through passageway 246 is effective to unseat the diaphragm 240 from the edge 218a of the cylinder 218 to dump pressurized fluid into the top of the main cylinder 218 and to drive the drive piston 226 through a drive stroke.

When the fastener driving tool is at rest, or during the return stroke of the drive piston, the upper open end of the cylinder 218 is exhausted to the atmosphere through the exhaust valve assembly 232. In the illustrated embodiment the exhaust valve assembly comprises a hollow valve stem 250 secured to the diaphragm connecting the upper end of the cylinder 218 to the atmosphere through a suitable exhaust passageway 252. However when the drive piston is operated through a fire or drive stroke, it is necessary for the upper end of the cylinder 218 to be closed, and to this end there is provided a valve seat 254 disposed adjacent the end of the valve stem 250 remote from the cylinder 218 and adapted to be engaged by the valve stem 250 when the diaphragm 240 is raised at the initiation of a drive stroke, thereby closing off the upper end of the cylinder 218 to the atmosphere.

To provide for the return drive of the fastener driving assembly 224, there is provided an air return chamber 260 continuously in communication with the fluid reservoir 216 through a plurality of ports 261 and defined by the volume contained between a large piston member 226b cooperatively engaged with a large cylinder portion 218b, and a small piston member 226c of reduced diameter from the large piston member 226b cooperating with a small cylinder portion 2180. Since the large upper cylinder portion 2l8b presents a larger effective area to the pressurized fluid within the air return chamber 260 than does the small piston member 226b, the drive piston 226 will continuously be biased upwardly toward its at rest position by the pressurized fluid within the air return chamber 260. It is however understood that when pressurized fluid is dumped into the open upper end of the cylinder 218, such pressurized fluid will be acting over a net piston area corresponding to the area of the small piston member 2260, and will be effective to drive the piston downwardly through its drive stroke. During such a driving stroke the return bias is a negligible force. The lower end of the cylinder 218 is exhausted to atmosphere in any suitable means, as by leakage between the driver blade member 228 and the walls of the drive track 236.

It will be understood that in the operation of the basic tool, the piston 226 and associated drive blade member 228 are driven downwardly through a drive stroke by connection of the open upper end 218a of the cylinder 218 with the reservoir 216. Since there is no significant restraint to the piston 226 during its downward movement, the effect of the return bias from the air return chamber 260 being negligible, the pressure above the piston 226 will be effective to drive the drive piston 226 through a drive stroke. Subsequent exhaustion of the open upper end 218a of the cylinder 218 to the atmosphere through the hollow valve stem 250 and exhaust passageway 252 will remove the downward drive force to the piston 226 and the return bias acting on the differential pistons 226b and 226c will return the drive piston 226 to its static or at rest position.

To cushion the drive stroke of the piston 226, there is provided a resilient annular bumper 274 at the lower end of the cylinder 218 which is engageable by the piston 226 as it reaches the end of its drive stroke.

Referring now to the control valve assembly 222, in accordance .with the present embodiment, the control valve assembly requires the cooperation of both a trigger 278 and a safety lever 280 to operate. Once either the trigger 278 or the safety lever 280 is positioned, the other can manipulate the cycle valve to fire the tool. Moreover in accordance with the present embodiment, the valve assembly 222 includes a singlecycle mechanism which is effective when the work piston has reached a predetermined position to return the work piston 226 to its normal or at rest position to condition the tool for a subsequent operation. Referring now specifically to the control valve assembly 222 the control valve assembly includes a valve housing 281 secured to the housing 212 of the tool 210 in any suitable manner such as by screw fasteners 281a. The valve housing 281 includes a valve cylinder 282. A valve body 284 is slideably received within the valve cylinder 282 and includes a valve body operator or stem 286 extending out of the valve cylinder 282 and engageable by oneof the control means, here shown as a safety lever 280, to shift the valve body 284 within the valve cylinder 282. In the illustrated embodiment, the safety lever 280 is provided with a bifurcated end 280a receiving the stem 286 to provide a lost motion connection between the safety lever 280 and the valve body 284. An adjustable stop 287 limits the outward movement of the valve body 284. The valve body 284 is closed at its lower end, as illustrated at 284a, FIG. 12,

to define a valve chamber 288. The other end of the valve body 284 is provided with an exhaust opening 284b opening to the atmosphere through the valve cylinder 282 and an exhaust port 290. The exhaust opening 284b is formed in part by an O-ring 292 defining a valve seat.

- A control or trigger valve element, here shown as a ball valve element 294, is normally seated on the valve seat 292 and separable therefrom upon actuation of both the control means, the trigger 278, and the safety lever 280. To this end the trigger valve 294 includes a trigger stem or valve operator 296 engageable against the ball valve element 294. A compression spring 297 biases the ball valve element 294 closed against the valve seat 292.

To define a plurality of passageway chambers between the valve body 284 and the valve cylinder 282, the valve piston 284 is provided with a plurality of sealing Orings 304, 306, 308 and 310 defining first, second and third passageway chambers 312, 314, and 316. The first passageway chamber 312 is always in communication with the cylinder valve assembly 220 through the passageway 248. The second passageway chamber 314 is always in communication with the fluid reservoir 216 through a passageway 318 defined in the housing 12, FIG. 10. The third passageway chamber 316 is connected to receive a signal as to the position of the piston 226 and, in the illustrated embodiment, is connected to a passageway 320 having a port 320a opening in the lower end of the cylinder 218 so as to be placed in communication with the air return chamber 260 when the lower piston member 226c moves downwardly sufficiently to clear the port 320a.

To provide for the snap acting of the piston 226, there is provided a single-cycle valve member 322, FIG. 12, positioned within the valve chamber 288. The valve member 322 contains a pair of spaced heads carrying two O-rings 326 and 328 each defining piston means on the valve member 322. A seepage passageway 330 communicates through the valve member 322 from between the spaced O-rings 326 and 328 into the upper end thereof opening into the upper portion of the valve chamber 288 so as to provide for a small seepage of fluid around the upper one of the piston means 326. Moreover the valve body 284 contains a first. opening or port 332 extending between an upper end portion 288a of the valve chamber 288 and the first passageway chamber 312 which is, therefore, normally in communication with the cylinder valve assembly 220 through the passageway 248. The valve body 284 is also provided with a second opening 334 extending between a central portion 288b of the valve chamber 288 and the second passageway chamber 314 which is, therefore, always in communication with the air reservoir 216 through the passageway 318. In addition, the valve body 284 contains a third opening 336 extending between a lower portion 288C of the valve chamber 288 and the third passageway 316 so that it may be placed in communication with the air return chamber 260 through the passageway 320 whenever the lower piston 226c moves below the passageway port 320a. The upper one of the valve heads carrying the O-ring 326 is positioned to cross over the first opening 332 in the valve piston 284 during the stroke of the valve member 322, while the lower one of the valve heads carrying the O-ring 328 is positioned intermediate the second and third openings 334 and 336 in the valve body 284 during the stroke of the valve member 322.

From the above detailed description, the operation of the improved control valve assembly is believed clear. However, briefly, when the fastener driving tool is at rest in the positions indicated in FIGS. 8 and 12, fluid from the reservoir 216 entering through the passageway 318 and opening 334 enters the valve chamber 288 and leaks around the valve head carrying the O-ring'326 through the seepage passageway 330, passing through the opening 332 into the first passageway chamber 312 and through the passageway 248 to provide pressurized fluid to the cylinder valve assembly 220 to maintain the valve closed.

When it is desired to fire the tool 210 through a work cycle, it is necessary to depress both the safety lever and the trigger 278 in order to unseat the ball valve element 294 from the valve seat 292. At this time the pressurized fluid from the valve cylinder assembly 220 is discharged through the passageway 248, passageway chamber 312, opening 332, around the ball valve element 294 and exhausted through the exhaust port 290. The seepage of pressurized fluid through the seepage passageway 330 is insufficient to appreciably affect the exhaust of fluid from the cylinder valve assembly 220. During the firing stroke the valve body 284 remains upwardly, the ball valve element 294 remains unseated from the valve seat 292, and the valve member 322 remains in its lower or downward position relative to the valve body 284. It will be understood that as the work piston 26 is driven downwardly, the lower piston 2260 will pass over the port 320a so as to place the passageway 320 in communication with the air return chamber 260. The pressure in the air return chamber is transmitted to the control valve assembly 222 through the passageway 320.

To provide for the snap-acting return of the work piston 226, as soon as a sufficient signal is received from the air return chamber 260 through the passageway 320, the pressure is transmitted into the lower end of the chamber 288 below the single-cycle valve member 322 through the third passageway chamber 316 and the third opening 336. This pressure is effective to move the single-cycle valve member 322 upwardly, and the upper O-ring 326 passes above the opening 332 communicating with the cylinder valve assembly 220. At this time pressurized fluid entering through the passageway 318 and second passageway chamber 314 will enter the valve body 284 through the second opening 334. The force of this pressure will be transmitted substantially unrestricted to the first opening 332 into the first passageway chamber 312 and through the passageway 248 to the cylinder valve assembly 220 to close the cylinder valve assembly 220 and permit return of the work piston 226 by the fluid in the air return chamber 260 acting on the differential areas of the upper and lower piston members 226b and 2260.

The single-cycle valve element 322 will remain in this return or upper position until such time as either the trigger 278 or safety lever 280 is released. At that time the components of the control valve assembly 222 will return to the normal or at rest position as illustrated in FIG. 12. More specifically, the seating of the ball valve 294 allows the compressed air supplied by the passageway 330 to accumulate above the piston means carrying the O-ring 326 to move the valve element 322 downwardly to its normal position as air leaks from below the piston means carrying the O-ring 328 due to leakage around the blade 228.

The tool 210 may be actuated by operation of both the trigger 278 and the safety lever 280. Moreover in a particular embodiment of the invention it was found that the valve element 296 had to be depressed only 0.010 inch or 0.015 inch to fire the tool. Therefore the lost motion connection between the valve body 284 and the safety lever 280 has been provided. The lost motion connection is dependent upon the length of the piston stem 286, and this lost motion connection permits recoil of the tool 210 from the workpiece and reengagement thereof without firing through the safety lever 280. In this connection, the resilient engagement of the O-rings 304, 306, 308, and 310 with the adjacent walls of the cylinder 282 is important in positively restraining or biasing the valve body 284 to remain in a position, either actuated or released, until positively moved to the alternate position by the safety lever 280.

The valve housing 281 is readily detachable from the remainder of the tool 210 by the mere removal of the fasteners 281a. To provide for continuation of the passageways 248, 318, and 320 between the housing 212 of the tool 210 and the valve housing 281, the valve housing 281 is provided with suitable elongated grooves, FIGS. 9 and 12, illustrated as 248a, 318a, and 320b formed in the valve housing 281 at the interface with the tool housing 212. Each of the grooves 248a, 318a, and 320b is sealed with suitable gaskets or other means such as the O-rings 339, 340, and 341. Thus, the entire control valve assembly 222 may be assembled with the remainder of the tool 210 as a unit to facilitate assembly, and may be removed and replaced as an assembly to facilitate servicing and replacement thereof.

Although this invention has been described with reference to diflerent embodiments thereof, numerous other modifications and embodiments will be devised by those skilled in the art which will fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly having two oppositely movable valve elements each mechanically coupled to a different one of said mechanisms so that the control valve assembly is operated only by joint mechanical actuation by both of said mechanisms, said control valve assembly being connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke when the control valve assembly is operated, said control valve assembly including a cycling valve connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said mechanisms.

2. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a cycling valve connected to retum said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said mechanisms, and means responsive to the position of said piston for providing a signal to control said cycling valve.

3. A pneumatically operated fastener driving tool as set forth in claim 2 including a piston return chamber and wherein said signal is provided from said piston return chamber.

4. A pneumatically operated fastener driving tool as set forth in claim 3 wherein said piston return chamber is defined between spaced piston members of a differential diameter drive piston, and wherein said signal is provided when the smaller one of said piston members passes over a signal port to place said single cycle valve in communication with said piston return chamber.

5. In a pneumatically operated fastener driving tool of the type including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, trigger control means for controlling the movement of the piston through a fastener driving stroke and safety control means responsive to a predetermined position of said tool relative to a workpiece, an improved control valve assembly comprising: valve cylinder defined in the housing, a valve body slideably received in said valve cylinder having an operator extending therefrom engageable by one of the control means to shift the valve body in said valve cylinder, said valve body being closed at one end to define a valve chamber and having an exhaust opening at the other end defining a valve seat, a control valve element in said chamber, a control valve element operator extending through said exhaust opening and operable by the other of said control means, said control valve element including a valve head normally seated on said valve seat and separable therefrom upon actuation of both of said control means, exhaust means for exhausting said exhaust opening .to the atmosphere, and first passage means placing said valve chamber in communication with said cylinder valve means.

6. The improved control valve as set forth in claim 5 including second passage means placing said valve chamber in communication with the fluid reservoir,

and means in said chamber operatively controlling fluid flow between said first and second passage means.

7. The improved control valve as set forth in claim' 6 includingsingle cycle means in said valve chamber connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of the control means.

8. The improved control valve as set forth in claim 6 wherein said valve body is provided with a plurality of rings defining a plurality of passageway chambers with said valve cylinder, the first passage means including a first one of said passageway chambers, and openings in said valve body, the second passage means including a second one of said passageway chambers and openings in said valve body, third passage means adapted to receive a cycling signal including a third one of said passageway chambers and openings in said valve body, and wherein said single cycle means includes a slideable single cycle valve stem member having a pair of spaced heads defining piston means, a first one of said piston means being movable to connect the first and second openings in said valve piston during its stroke, said second one of said piston means being positioned intermediate the second and third openings in said valve body during the stroke thereof and forming a pneumatic seal across said valve chamber.

9. The improved control valve as set forth in claim 8 wherein the pneumatically operated fastener driving tool includes a pneumatic piston return chamber, the third passage means communicating with said piston retum chamber.

10. The control valve set forth in claim 8 including piston means and between the first and second openings in the valve body.

1 1. The improved control valve as set forth in claim 5 including a lost motion connection on the one of said operators engageable by the safety control means.

12. The improved control valve as set forth in claim 4 wherein said first passage means includes an additional valve seat in said first passage means between the chamber and the cylinder valve means, and said control valve element includes a valve portion normally separated from said additional valve seat and seatable thereon upon relative depression of said control valve element and said valve body.

13. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, trigger control means for controlling the movement of the piston through a fastener driving stroke, safety control means responsive to a predetermined position of the tool relative to the workpiece, and a control valve assembly including a valve housing detachably secured to the first mentioned housing as a unit, said control valve assembly being responsive only to joint actuation by both said control means and connected to control said cylinder valve means.

14. A pneumatically operated fastener driving tool as set forth in claim 13 wherein said control valve. assembly includes a single cycle valve connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said control means.

15. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a pair of generally axially aligned and oppositely movable valve elements, one of which is coupled to and actuated in one direction by the trigger mechanism and the other of which is coupled to and actuated in a direction opposite to said one direction by the safety mechanism.

16. The pneumatically operated fastener driving tool as set forth in claim including biasing means coupling the pair of valve elements for conjoint movement under actuation by one of said mechanisms, the biasing means being overcome by actuation by the other of said mechanisms to move the pair of valve elements relative to each other.

17. The pneumatically operated fastener driving tool as set forth in claim 15 in which the control valve assembly includes a third valve element movable relative to the pair of valve elements to provide a cycling valve for returning the piston to its normal position after the fastener driving stroke.

18. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a pair of relatively movable valve elements, one of which is coupled to and actuated by the trigger mechanism and the other of which is coupled to and actuated by the safety mechanism, said valve element actuated by the safety mechanism being biased to remain in both its actuated and its unactuated positions, and said safety mechanism being coupled to this valve element by a lost motion connection.

19. The pneumatically operated fastener driving tool set forth in claim 18 in which the valve element is biased by at least one resilient O-ring.

20. A pneumatically operated fastener driving tool including a tool housing having a cavity defining a fluid reservoir; a cylinder in the tool housing; a piston slideably mounted in the cylinder; fluid operated main valve means for selectively coupling the cylinder to the atmosphere and the reservoir to operate the piston; a manually operable and movably mounted trigger; said tool housing including an external'coupling surface remote from the main valve means and adjacent the trigger; passages in said tool housing connecting with the reservoir and the main valve means, each of said passages having a port coupled to the passage and terminating in said external couplingsurface of said tool housing; and control means detachably secured as a unit externally to said housing and providing the fluid controls for controlling the main valve means to control the movement of said piston in said cylinder, said control means including a control housing, at least one fluid control valve means in the control housing with a valve operator projecting from the control housing adjacent the trigger for operation by the trigger, a control housing coupling surface, and passages in the control housing communicating with the fluid control valve means and the ports in said control housing coupling surface, said control housing being detachably secured to the tool housing with the tool and control housing coupling surfaces adjacent each other and the ports in the tool and control housing surfaces in communication.

21. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a cylinder valve means for controlling the admission of fluid and the exhaustion of fluid from one end of the cylinder, a pneumatic piston return system including a return air chamber for returning said piston, control valve means actuated from a first position to a second position in response to the pressure in the return air chamber when the piston is moved to a given position and connected to said cylinder valve means, movement of said control valve means to said second position operating the cylinder valve means to close said one end of said cylinder to said reservoir and to exhaust -the one end of the cylinder, and pilot valve means connected to said cylinder valve and said control valve means and operable between first and second positions, movement of said pilot valve means to said first position controlling the cylinder valve means to initiate admission of fluid into said one end of said cylinder, movement of said pilot valve means to said second position controlling said control valve to move said control valve means from its second position to its first position.

22. A fastener driving tool comprising a housing having a reservoir adapted to be continuously supplied with pressurized fluid and containing a cylinder having an open end in communication with the reservoir, fastener driving means including a piston slideably mounted in the cylinder, cylinder valve means normally engaging the open end of the cylinder to prevent communication between the reservoir and the cylinder, fluid operated means for separating the cylinder and the cylinder valve means to admit fluid to the cylinder to drive the piston from a normal position to a displaced position and for returning the cylinder and the cylinder valve means to an engaged position, piston return means for moving the piston from the displaced position to the normal position when the cylinder and cylinder valve means are in engagement, and a control assembly connected to the fluid operated means for selectively supplying fluid from the reservoir to the fluid operated means and for connecting the fluid operated means to the atmosphere to control the operation of the fluid operated means, said control assembly including a mechanically operated valve means operable from a normal position to a displaced position to control the fluid operated means to separate the cylinder and the cylinder valve means, said control assembly also including a fluid operated valve means operable from a normal position to a displaced position when the mechanically operated valve means is in its displaced position for controlling the fluid operated means to return the cylinder and the cylinder valve means to their engaged position thereby cycling the piston through a complete cycle, said control assembly also including a passageway for supplying fluid to the fluid operated valve means when the piston moves to its displaced position to move the fluid operated valve means from its normal position to its displaced position, the operation of said mechanically operated valve means from its displaced position to its normal position controlling movement of the fluid operated valve means from its displaced position to its normal position.

23. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a cylinder valve means for controlling the admission of fluid and the exhaustion of fluid from one end of the cylinder, a pneumatic piston return system in said housing connected to provide fluid for the return stroke in said piston, control valve means operated from a first to a second position by said pneumatic piston return system and connected to said cylinder valve means to close said one end of said cylinder to said reservoir and to exhaust the one end of the cylinder when the control valve means is in its second position thereby cycling said piston through a complete cycle, and pilot valve means connected to said cylinder valve and operable to a first position to initiate admission of fluid into said one end of said cylinder and connected to said control valve and operable to a second position to move said control valve means from its second position to its first position.

24. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve having first and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, a first passage means for supplying pressurized fluid to the cylinder valve means, a second passage means for exhausting pressurized fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to the cylinder valve means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to one of its spaced first and second positions, and means including a manually actuated pilot valve means for controlling the application of fluid from the reservoir to the second fluid responsive surface on the reciprocable control valve to effect movement of the reciprocable control valve to the other of its spaced first and second positions.

25. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve having first and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, spaced first and second passage means for supplying fluid to and exhausting fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to the cylinder valve means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to one of its spaced first and second positions, and means including a manually actuated pilot valve means and a given one of said first and second passage means for controlling the application of fluid from the reservoir to the second fluid responsive surface on the reciprocable control valve to effect movement of the reciprocable control valve to the other of its spaced first and second positions.

26. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve havingfirst and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, a common passage means for coupling the reciprocable control valve to the cylinder valve means, spaced first and second passage means for supplying fluid to and for exhausting fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to the common passage means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to its first position, movement of the reciprocable control valve to its first position effecting closure of the cylinder valve means to exhaust fluid from the cylinder, means for supplying fluid to the second fluid pressure responsive surface on the reciprocable control valve which is effective to move the reciprocable control valve to its second position after the fluid from the first fluid pressure responsive surface has been exhausted by closure of the cylinder valve means, and a manually actuated valve connected in series with one of said first and second passage means and the reciprocable control valve and both the atmosphere and the reservoir, the manually actuated valve being operable to alternate settings to alternately connect the connected one of the first and second passage means to the atmosphere and the fluid in the reservoir independent of the position of the reciprocable control valve.

27. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir; a cylinder in said housing; a piston slideably mounted in the cylinder; cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of said cylinder in response to the exhaustion of fluid from said cylinder valve and the admission of fluid from said reservoir to said cylinder valve means; a cycling control valve; first passage means connecting said cycling control valve to said cylinder valve means; second passage means connecting said cycling valve to said cylinder; third passage means connecting said cycling valve to said reservoir; fourth passage means connected to said cycling valve; and a trigger valve connected to said cycling control valve through said fourth passage means effective when depressed to exhaust said cycling control valve and when released to permit fluid from the reservoir to accumulate in said cycling control valve; said cycling valve including a valve element shiftable by the pressure buildup in said second passage means between a normal position connecting said first and fourth passage means and an operated position connecting said first and third passage means.

28. A fastener driving tool as set forth in claim 27 wherein said valve element is a fluid pressure operated valve movable to said normal position by the pressure in said reservoir accumulated under the control of the released trigger valve and movable to said operated position by fluid pressure admitted to said cylinder.

29. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and exhaustion of fluid from one end of the cylinder, control valve means coupled to the cylinder valve means for controlling the operation of the cylinder valve means, and operating means for operating the control valve means, said operating means including a manually operable trigger means and a safety means normally in an inoperative position and movable between the inoperative position and an operative position in dependence on the positioning of the tool adjacent a workpiece, the trigger means and the safety means being mechanically coupled to the control valve means and operating the control valve means only when the trigger means is actuated and the safety means is moved to its operative position, the safety means having a lost motion means so that a portion only of the movement imparted to the safety means by engagement of the workpiece is effective to control operation of the control valve means to jointly with actuation of the trigger means and so that the initial restoring movement of the safety means toward the inoperative position is not effective to release the control valve means.

30. A pneumatically operated fastener driving tool as set forth in claim 29 and including a cycling valve means connected to return said piston to its normal position after the completion of a fastener driving stroke. regardless of the condition of said operating g l i A fluid operated fastener driving tool comprising a housing, a cylinder in the housing, a piston slideably mounted in the cylinder, fluid actuated cylinder valve means controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a single control valve for controlling the application of fluid to the cylinder valve means to control the operation of the cylinder valve means, and operating means mechanically coupled to the control valve for operating the control valve, said operating means including a manually actuated trigger movable between operated and released positions, said operating means also including safety means operated from a released position to an operated position by placing the tool adjacent a workpiece, the control valve being operated to control the opening of the cylinder valve means only when the trigger is in its operated position and the safety means is in its operated position, said safety means including both a workpiece engaging means movable from a normal position to a displaced position to actuate the safety means to its operated position and a lost motion coupling to the workpiece engaging means to permit the workpiece engaging means to move a given distance away from its displaced position toward its normal position without actuating the safety means to its released position. 

1. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly having two oppositely movable valve elements each mechanically coupled to a different one of said mechanisms so that the control valve assembly is operated only by joint mechanical actuation by both of said mechanisms, said control valve assembly being connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke when the control valve assembly is operated, said control valve assembly including a cycling valve connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said mechanisms.
 2. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a cycling valve connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said mechanisms, and means responsive to the position of said piston for providing a signal to control said cycling valve.
 3. A pneumatically operated fastener driving tool as set forth in claim 2 including a piston return chamber and wherein said signal is provided from said piston return chamber.
 4. A pneumatically operated fastener driving tool as set forth in claim 3 wherein said piston return chamber is defined between spaced piston members of a differential diameter drive piston, and wherein said signal is provided when the smaller one of said piston members passes over a signal port to place said single cycle valve in communication with said piston return chamber.
 5. In a pneumatically operated fastener driving tool of the type including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, trigger control means for controlling the movement of the piston through a fastener driving stroke and safety control means responsive to a predetermined position of said tool relative to a workpiece, an improved control valve assembly comprising: valve cylinder defined in the housing, a valve body slideably received in said valve cylinder having an operator extending therefrom engageable by one of the control means to shift the valve body in said valve cylinder, said valve body being closed at one end to define a valve chamber and having an exhaust opening at the other end defining a valve seat, a control valve element in said chamber, a control valve element operator extending through said exhaust opening and operable by the other of said control means, said control valve element including a valve head normally seated on said valve seat and separable therefrom upon actuation of both of said control means, exhaust means for exhausting said exhaust opening to the atmosphere, and first passage means placing said valve chamber in communication with said cyLinder valve means.
 6. The improved control valve as set forth in claim 5 including second passage means placing said valve chamber in communication with the fluid reservoir, and means in said chamber operatively controlling fluid flow between said first and second passage means.
 7. The improved control valve as set forth in claim 6 including single cycle means in said valve chamber connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of the control means.
 8. The improved control valve as set forth in claim 6 wherein said valve body is provided with a plurality of rings defining a plurality of passageway chambers with said valve cylinder, the first passage means including a first one of said passageway chambers, and openings in said valve body, the second passage means including a second one of said passageway chambers and openings in said valve body, third passage means adapted to receive a cycling signal including a third one of said passageway chambers and openings in said valve body, and wherein said single cycle means includes a slideable single cycle valve stem member having a pair of spaced heads defining piston means, a first one of said piston means being movable to connect the first and second openings in said valve piston during its stroke, said second one of said piston means being positioned intermediate the second and third openings in said valve body during the stroke thereof and forming a pneumatic seal across said valve chamber.
 9. The improved control valve as set forth in claim 8 wherein the pneumatically operated fastener driving tool includes a pneumatic piston return chamber, the third passage means communicating with said piston return chamber.
 10. The control valve set forth in claim 8 including means for bleeding fluid around the first one of the piston means and between the first and second openings in the valve body.
 11. The improved control valve as set forth in claim 5 including a lost motion connection on the one of said operators engageable by the safety control means.
 12. The improved control valve as set forth in claim 4 wherein said first passage means includes an additional valve seat in said first passage means between the chamber and the cylinder valve means, and said control valve element includes a valve portion normally separated from said additional valve seat and seatable thereon upon relative depression of said control valve element and said valve body.
 13. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, trigger control means for controlling the movement of the piston through a fastener driving stroke, safety control means responsive to a predetermined position of the tool relative to the workpiece, and a control valve assembly including a valve housing detachably secured to the first mentioned housing as a unit, said control valve assembly being responsive only to joint actuation by both said control means and connected to control said cylinder valve means.
 14. A pneumatically operated fastener driving tool as set forth in claim 13 wherein said control valve assembly includes a single cycle valve connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said control means.
 15. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a pair of generally axially aligned and oppositely movable valve elements, one of which is coupled to and actuated in one direction by the trigger mechanism and the other of which is coupled to and actuated in a direction opposite to said one direction by the safety mechanism.
 16. The pneumatically operated fastener driving tool as set forth in claim 15 including biasing means coupling the pair of valve elements for conjoint movement under actuation by one of said mechanisms, the biasing means being overcome by actuation by the other of said mechanisms to move the pair of valve elements relative to each other.
 17. The pneumatically operated fastener driving tool as set forth in claim 15 in which the control valve assembly includes a third valve element movable relative to the pair of valve elements to provide a cycling valve for returning the piston to its normal position after the fastener driving stroke.
 18. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of the cylinder, a mechanically actuated trigger mechanism, a mechanically actuated safety mechanism responsive to a predetermined position of the tool relative to a workpiece, and a single control valve assembly coupled to both of said mechanisms to be responsive only to joint mechanical actuation by both of said mechanisms and connected to control said cylinder valve means to admit fluid from the reservoir to the cylinder to operate the piston through a fastener driving stroke, said control valve assembly including a pair of relatively movable valve elements, one of which is coupled to and actuated by the trigger mechanism and the other of which is coupled to and actuated by the safety mechanism, said valve element actuated by the safety mechanism being biased to remain in both its actuated and its unactuated positions, and said safety mechanism being coupled to this valve element by a lost motion connection.
 19. The pneumatically operated fastener driving tool set forth in claim 18 in which the valve element is biased by at least one resilient O-ring.
 20. A pneumatically operated fastener driving tool including a tool housing having a cavity defining a fluid reservoir; a cylinder in the tool housing; a piston slideably mounted in the cylinder; fluid operated main valve means for selectively coupling the cylinder to the atmosphere and the reservoir to operate the piston; a manually operable and movably mounted trigger; said tool housing including an external coupling surface remote from the main valve means and adjacent the trigger; passages in said tool housing connecting with the reservoir and the main valve means, each of said passages having a port coupled to the passage and terminating in said external coupling surface of said tool housing; and control means detachably secured as a unit externally to said housing and providing the fluid controls for controlling the main valve means to control the movement of said piston in said cylinder, said control means including a control housing, at least one fluid control valve means in the control housing with a valve operator projecting from the control housing adjacent the trigger for operation by the trigger, a control housing coupling surface, and passages in the control housing communicating with the fluid control valve means and the ports in said control housing coupling surface, said control housing being detachably secured to the tool housing with the tool and controL housing coupling surfaces adjacent each other and the ports in the tool and control housing surfaces in communication.
 21. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a cylinder valve means for controlling the admission of fluid and the exhaustion of fluid from one end of the cylinder, a pneumatic piston return system including a return air chamber for returning said piston, control valve means actuated from a first position to a second position in response to the pressure in the return air chamber when the piston is moved to a given position and connected to said cylinder valve means, movement of said control valve means to said second position operating the cylinder valve means to close said one end of said cylinder to said reservoir and to exhaust the one end of the cylinder, and pilot valve means connected to said cylinder valve and said control valve means and operable between first and second positions, movement of said pilot valve means to said first position controlling the cylinder valve means to initiate admission of fluid into said one end of said cylinder, movement of said pilot valve means to said second position controlling said control valve to move said control valve means from its second position to its first position.
 22. A fastener driving tool comprising a housing having a reservoir adapted to be continuously supplied with pressurized fluid and containing a cylinder having an open end in communication with the reservoir, fastener driving means including a piston slideably mounted in the cylinder, cylinder valve means normally engaging the open end of the cylinder to prevent communication between the reservoir and the cylinder, fluid operated means for separating the cylinder and the cylinder valve means to admit fluid to the cylinder to drive the piston from a normal position to a displaced position and for returning the cylinder and the cylinder valve means to an engaged position, piston return means for moving the piston from the displaced position to the normal position when the cylinder and cylinder valve means are in engagement, and a control assembly connected to the fluid operated means for selectively supplying fluid from the reservoir to the fluid operated means and for connecting the fluid operated means to the atmosphere to control the operation of the fluid operated means, said control assembly including a mechanically operated valve means operable from a normal position to a displaced position to control the fluid operated means to separate the cylinder and the cylinder valve means, said control assembly also including a fluid operated valve means operable from a normal position to a displaced position when the mechanically operated valve means is in its displaced position for controlling the fluid operated means to return the cylinder and the cylinder valve means to their engaged position thereby cycling the piston through a complete cycle, said control assembly also including a passageway for supplying fluid to the fluid operated valve means when the piston moves to its displaced position to move the fluid operated valve means from its normal position to its displaced position, the operation of said mechanically operated valve means from its displaced position to its normal position controlling movement of the fluid operated valve means from its displaced position to its normal position.
 23. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a cylinder valve means for controlling the admission of fluid and the exhaustion of fluid from one end of the cylinder, a pneumatic piston return system in said housing connected to provide fluid for the return stroke in said piston, control valve means operated from a first to a second position by said pneumatic piston return system and conneCted to said cylinder valve means to close said one end of said cylinder to said reservoir and to exhaust the one end of the cylinder when the control valve means is in its second position thereby cycling said piston through a complete cycle, and pilot valve means connected to said cylinder valve and operable to a first position to initiate admission of fluid into said one end of said cylinder and connected to said control valve and operable to a second position to move said control valve means from its second position to its first position.
 24. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve having first and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, a first passage means for supplying pressurized fluid to the cylinder valve means, a second passage means for exhausting pressurized fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to the cylinder valve means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to one of its spaced first and second positions, and means including a manually actuated pilot valve means for controlling the application of fluid from the reservoir to the second fluid responsive surface on the reciprocable control valve to effect movement of the reciprocable control valve to the other of its spaced first and second positions.
 25. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve having first and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, spaced first and second passage means for supplying fluid to and exhausting fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to the cylinder valve means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to one of its spaced first and second positions, and means including a manually actuated pilot valve means and a given one of said first and second passage means for controlling the application of fluid from the reservoir to the second fluid responsive surface on the reciprocable control valve to effect movement of the reciprocable control valve to the other of its spaced first and second positions.
 26. A fluid operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slideably mounted in said cylinder, a fluid operated cylinder valve means for controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a reciprocable control valve having first and second fluid pressure responsive surfaces for moving the valve in opposite directions between spaced first and second positions, a common passage means for coupling the reciprocable control valve to the cylinder valve means, spaced first and second passage means for supplying fluid to and for exhausting fluid from the cylinder valve means, said reciprocable control valve coupling different ones of the first and second passage means to tHe common passage means in its first and second positions, third passage means for supplying fluid after the opening of the cylinder valve means to the first fluid pressure responsive surface on the reciprocable control valve to move this valve to its first position, movement of the reciprocable control valve to its first position effecting closure of the cylinder valve means to exhaust fluid from the cylinder, means for supplying fluid to the second fluid pressure responsive surface on the reciprocable control valve which is effective to move the reciprocable control valve to its second position after the fluid from the first fluid pressure responsive surface has been exhausted by closure of the cylinder valve means, and a manually actuated valve connected in series with one of said first and second passage means and the reciprocable control valve and both the atmosphere and the reservoir, the manually actuated valve being operable to alternate settings to alternately connect the connected one of the first and second passage means to the atmosphere and the fluid in the reservoir independent of the position of the reciprocable control valve.
 27. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir; a cylinder in said housing; a piston slideably mounted in the cylinder; cylinder valve means controlling admission of fluid to and the exhaustion of fluid from one end of said cylinder in response to the exhaustion of fluid from said cylinder valve and the admission of fluid from said reservoir to said cylinder valve means; a cycling control valve; first passage means connecting said cycling control valve to said cylinder valve means; second passage means connecting said cycling valve to said cylinder; third passage means connecting said cycling valve to said reservoir; fourth passage means connected to said cycling valve; and a trigger valve connected to said cycling control valve through said fourth passage means effective when depressed to exhaust said cycling control valve and when released to permit fluid from the reservoir to accumulate in said cycling control valve; said cycling valve including a valve element shiftable by the pressure buildup in said second passage means between a normal position connecting said first and fourth passage means and an operated position connecting said first and third passage means.
 28. A fastener driving tool as set forth in claim 27 wherein said valve element is a fluid pressure operated valve movable to said normal position by the pressure in said reservoir accumulated under the control of the released trigger valve and movable to said operated position by fluid pressure admitted to said cylinder.
 29. A pneumatically operated fastener driving tool including a housing having a cavity defining a fluid reservoir, a cylinder in the housing, a piston slideably mounted in the cylinder, cylinder valve means controlling admission of fluid to and exhaustion of fluid from one end of the cylinder, control valve means coupled to the cylinder valve means for controlling the operation of the cylinder valve means, and operating means for operating the control valve means, said operating means including a manually operable trigger means and a safety means normally in an inoperative position and movable between the inoperative position and an operative position in dependence on the positioning of the tool adjacent a workpiece, the trigger means and the safety means being mechanically coupled to the control valve means and operating the control valve means only when the trigger means is actuated and the safety means is moved to its operative position, the safety means having a lost motion means so that a portion only of the movement imparted to the safety means by engagement of the workpiece is effective to control operation of the control valve means jointly with actuation of the trigger means and so that the initial restoring movement of the safety means toward the inoperative position is not effective to releaSe the control valve means.
 30. A pneumatically operated fastener driving tool as set forth in claim 29 and including a cycling valve means connected to return said piston to its normal position after the completion of a fastener driving stroke regardless of the condition of said operating means.
 31. A fluid operated fastener driving tool comprising a housing, a cylinder in the housing, a piston slideably mounted in the cylinder, fluid actuated cylinder valve means controlling the admission of fluid to and the exhaustion of fluid from one end of the cylinder, a single control valve for controlling the application of fluid to the cylinder valve means to control the operation of the cylinder valve means, and operating means mechanically coupled to the control valve for operating the control valve, said operating means including a manually actuated trigger movable between operated and released positions, said operating means also including safety means operated from a released position to an operated position by placing the tool adjacent a workpiece, the control valve being operated to control the opening of the cylinder valve means only when the trigger is in its operated position and the safety means is in its operated position, said safety means including both a workpiece engaging means movable from a normal position to a displaced position to actuate the safety means to its operated position and a lost motion coupling to the workpiece engaging means to permit the workpiece engaging means to move a given distance away from its displaced position toward its normal position without actuating the safety means to its released position. 